Apparatus and Methods for Adaptively Using Signals to Control a Semiconductor Optical Amplifier (SOA)

ABSTRACT

An apparatus comprising an optical power splitter, an optical delay line coupled to the optical power splitter, an optical amplifier (OA) coupled to the optical delay line, and an adaptive injection current (AIC) controller coupled to the optical power splitter and the OA. Also disclosed is an apparatus comprising at least one component configured to implement a method comprising converting an optical signal into a voltage signal, calculating an amplitude correction value for the voltage signal, inverting an amplitude of the voltage signal, adjusting the amplitude of the inverted voltage signal according to the amplitude correction value, and converting the adjusted voltage signal into a current signal. Included is a network comprising an optical line terminal (OLT) comprising an optical receiver and an AIC controlled OA coupled to the optical receiver, wherein the AIC controlled OA provides optical power equalization for any upstream optical signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/046,294, filed Mar. 11, 2008 by Yuxin Dai, and entitled“Adaptive Injection Current Controlled Burst Mode SOA for Long and WideReach High Speed PON,” which is incorporated herein by reference as ifreproduced in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

A passive optical network (PON) is one system for providing networkaccess over “the last mile.” The PON is a point to multi-point networkcomprised of an optical line terminal (OLT) at the central office, anoptical distribution network (ODN), and a plurality of optical networkunits (ONUs) at the customer premises. In current PON systems, thedownstream data is broadcasted with no or infrequent interruptions fromthe OLT to the ONUs in the form of about continuous optical wavesignals. On the other hand, the upstream data is transmitted from theONUs to the OLT with more frequent interruptions or pauses in the formof optical burst signals. The optical burst signals' amplitudes can varyfrom one optical burst signal to another. As a result of the frequentpauses and the variations in the individual optical burst signalsamplitudes, the average amplitude in the optical burst signals canfluctuate over time that results in DC voltage offset variation in theoptical receiver. The varying DC offset can increase the time requiredby the optical receivers to adjust the decision threshold anddistinguish between the individual “0” and “1” symbols, referred aslevel recovery. The excessive time required for level recovery in theoptical receivers can reduce the optical receivers' detectioncapabilities as the optical burst signal rates increase, for example,from about 1.25 Gigabits per second (Gbps) to about 2.5 Gbps and about10 Gbps.

An 8b10b code can be implemented to relax the optical receiver's timerequirements, where eight-bit blocks of random data can be convertedinto ten-bit blocks of restricted code. However, the 8b10b code addsabout a 25 percent bandwidth overhead. Alternatively, optical powerequalization methods can be implemented using optical amplifiers (OAs),such as gain clamped Semiconductor OAs (SOAs), to smooth the opticalburst signal to some degrees thus to reduce the DC offset variations inthe optical receiver. The SOAs can also amplify the optical burstsignals and compensate for transmission losses, which may result due tosignal splitting in the ODN, signal attenuation over long traveldistances, or both. However, optical power equalization using opticalinjection to the SOAs or using inversed input signal directly superposedon the bias current of SOAs becomes less efficient when the burstamplitude difference in the optical burst signals increase.

SUMMARY

In one embodiment, the disclosure includes an apparatus comprising anoptical power splitter, an optical delay line coupled to the opticalpower splitter, an OA coupled to the optical delay line, and an adaptiveinjection current (AIC) controller coupled to the optical power splitterand the OA.

In another embodiment, the disclosure includes an apparatus comprisingat least one component configured to implement a method comprisingconverting an optical signal into a voltage signal, calculating anamplitude correction value for the voltage signal, inverting anamplitude of the voltage signal, adjusting the amplitude of the invertedvoltage signal according to the amplitude correction value, andconverting the adjusted voltage signal into a current signal.

In yet another embodiment, the disclosure includes a network comprisingan OLT comprising an optical receiver and an AIC controlled OA coupledto the optical receiver, wherein the AIC controlled OA provides opticalpower equalization for any upstream optical signals.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a schematic diagram of an embodiment of a PON.

FIG. 2 is a schematic diagram of an embodiment of an adaptive injectioncurrent controlled OA.

FIG. 3 is a schematic diagram of an embodiment of an optical booster.

FIG. 4 is a schematic diagram of an embodiment of an integrated opticalreceiver.

FIG. 5 is a schematic diagram of an embodiment of a long & wide-reachOLT.

FIG. 6 is a schematic diagram of an embodiment of a long & wide-reachPON.

FIG. 7 is a schematic diagram of another embodiment of a long &wide-reach PON.

FIG. 8 is a flowchart of an embodiment of an adaptive injection currentcontrolled optical burst mode method.

FIG. 9 is a schematic diagram of an embodiment of adaptive injectioncurrent controlled optical burst signals.

FIG. 10 is a schematic diagram of one embodiment of a general-purposecomputer system.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

Disclosed herein is an apparatus and method for implementing adaptiveoptical power equalization using OAs to smooth the optical burst signaltherefore to eliminate or reduce DC offset variations in the opticalreceiver. The OAs may be SOAs that may be injected with current controlsignals in an adaptive manner to amplify and forward the optical burstsignals at about equal power. The injected current control signals maybe obtained by tapping into the transmitted optical burst signals,converting a portion of the optical burst signals into electricalsignals, adaptively reshaping the electrical signals, and converting thereshaped electrical signals into current control signals. An electricalsignal may be adaptively reshaped by comparing the amplitude of theelectrical signal to the amplitudes of previous electrical signalscorresponding to previous optical burst signals, and adjusting theamplitude accordingly. The apparatus may be implemented to boost thetransmitted optical signals along a PON, to receive the signals at about10 Gbps rates using standard optical receivers in the PON, and totransmit and receive the signals over long distances and in PONscomprising many ONUs.

FIG. 1 illustrates one embodiment of a PON 100. The PON 100 comprises anOLT 110, a plurality of ONUs 120, and an ODN 130. The PON 100 is acommunications network that does not require any active components todistribute data between the OLT 110 and the ONUs 120. Instead, the PON100 uses the passive optical components in the ODN 130 to distributedata between the OLT 110 and the ONUs 120. Examples of suitable PONs 100include the asynchronous transfer mode PON (APON) and the broadband PON(BPON) defined by the ITU-T G.983 standard, the Gigabit PON (GPON)defined by the ITU-T G.984 standard, the Ethernet PON (EPON) defined bythe IEEE 802.3ah standard, 10 Gbps PON, and the wavelength divisionmultiplexing PON (WPON), all of which are incorporated by reference asif reproduced in their entirety.

One component of the PON 100 may be the OLT 110. The OLT 110 may be anydevice that is configured to communicate with the ONUs 120 and anothernetwork (not shown). Specifically, the OLT 110 may act as anintermediary between the other network and the ONUs 120. For instance,the OLT 110 may forward data received from the network to the ONUs 120,and forward data received from the ONUs 120 onto the other network.Although the specific configuration of the OLT 110 may vary depending onthe type of PON 100, in an embodiment, the OLT 110 may comprise atransmitter and a receiver, as explained in detail below. When the othernetwork is using a protocol, such as Ethernet or SONET/SDH, that isdifferent from the communications protocol used in the PON 100, the OLT110 may comprise a converter that converts the other network's data intothe PON's protocol. The OLT 110 converter may also convert the PON'sdata into the other network's protocol. The OLT 110 described herein istypically located at a central location, such as a central office, butmay be located at other locations as well.

Another component of the PON 100 may be the ONUs 120. The ONUs 120 maybe any devices that are configured to communicate with the OLT 110 and acustomer or user (not shown). Specifically, the ONUs may act as anintermediary between the OLT 110 and the customer. For instance, theONUs 120 may forward data received from the OLT 110 to the customer, andforward data received from the customer onto the OLT 110. Although thespecific configuration of the ONUs 120 may vary depending on the type ofPON 100, in an embodiment, the ONUs 120 may comprise an opticaltransmitter configured to send optical signals to the OLT 110.Additionally, the ONUs 120 may comprise an optical receiver configuredto receive optical signals from the OLT 110 and a converter thatconverts the optical signal into electrical signals for the customer,such as signals in the Asynchronous Transfer Mode (ATM) or Ethernetprotocol. The ONUs 120 may also comprise a second transmitter and/orreceiver that may send and/or receive the electrical signals to acustomer device. In some embodiments, ONUs 120 and optical networkterminals (ONTs) are similar, and thus the terms are usedinterchangeably herein. The ONUs are typically located at distributedlocations, such as the customer premises, but may be located at otherlocations as well.

Another component of the PON 100 may be the ODN 130. The ODN 130 is adata distribution system that may comprise optical fiber cables,couplers, splitters, distributors, and/or other equipment. In anembodiment, the optical fiber cables, couplers, splitters, distributors,and/or other equipment are passive optical components. Specifically, theoptical fiber cables, couplers, splitters, distributors, and/or otherequipment may be components that do not require any power to distributedata signals between the OLT 110 and the ONUs 120. The ODN 130 typicallyextends from the OLT 110 to the ONUs 120 in a branching configuration asshown in FIG. 1, but may be alternatively configured in any otherconfiguration.

FIG. 2 illustrates an embodiment of an AIC controlled OA 200, which maybe coupled to the OLT 110 or the ODN 130 in the PON 100. The AICcontrolled OA 200 may be used to eliminate or reduce the burst amplitudedifference in the optical burst signals hence reduce the DC offsetvariations in the optical receiver. The AIC controlled OA 200 may alsobe used to compensate for signal attenuations and losses by boostingoptical signal strength. The AIC controlled OA 200 may comprise anoptical power splitter 210, an optical delay line (ODL) 220, an OA 230,and an AIC controller 240.

The optical power splitter 210 may be any device such as afused-biconic-taper (FBT) or planar-lightwave-circuit (PLC) that may beused to split an incoming light beam into a plurality of light beams.The optical power splitter 210 may receive optical signals and split theoptical signals into two copies. The optical power splitter 210 may becoupled to the ODL 220 and may forward a first copy of the opticalsignals to the ODL 220. The optical power splitter 210 may also becoupled to the AIC controller 240 and may forward a second copy of theoptical signals to the AIC controller 240. The two copies may have atotal power that may be about equal to the power of the received opticalsignals. The power of the first copy may also be larger than that of thesecond copy.

The ODL 220 may be coupled to the OA 230 in addition to the opticalpower splitter 210. The ODL 220 may receive the first copy of theoptical signal from the optical power splitter 210, delay the traveltime of the first copy, and forward the first copy to the OA 230.Specifically, the ODL 220 may comprise input and output opticalcollimators separated by some adjustable space distance. The inputcollimator may receive the first copy in the fiber coupled to the ODL220 and send the first copy through the space between the input andoutput collimators and to the output collimator. The output collimatormay receive the first copy and send the first copy to the fiber coupledto the OA 230. The travel delay time of the first copy between the inputand output collimators may be increased or decreased by increasing ordecreasing, respectively, the space distance between the input andoutput collimators. The ODL 220 may also comprise a spool of opticalfiber of certain lengths that are determined by the required value ofdelay time.

The OA 230 may be any optical amplifier, such as an optical amplifiercomprising a semiconductor gain medium with anti-reflection elements attwo opposite edge surfaces. The semiconductor gain medium may be pumpedor injected electrically using current signals to amplify the opticalsignals inside the OA 230. The optical signal may also be amplifiedproportionally to the injection current signals if the OA is operated inthe linear region. The OA 230 may be coupled to the AIC controller 240and may receive the injection current signals from the AIC controller240. Specifically, the OA 230 may receive the first copy of the opticalsignals from the ODL 220 at one input and injection currents from theAIC controller 240 at another input. The OA 230 may amplify the power ofthe optical signals proportionally to the amplitude of the injectioncurrents and forward the amplified optical signal downstream.

The AIC controller 240 may receive the second copy of the opticalsignals from the optical power splitter 210 and adaptively convert theoptical signals into the injection currents, which may then be injectedinto the OA 230. The injection currents may be controlled to amplify thefirst copy of optical burst signals in the OA 230 at about equal powerand with no or reduced DC offset variations when detected with anoptical receiver. Specifically, the AIC controller 240 may send theinjection currents to the OA 230 at about the same arrival time as thefirst copy of optical signals, which may be delayed by the ODL 220. Thedelay time may be about equal to the time required by the AIC controller240 to convert the second copy of the optical signals into the injectioncurrents. The AIC controller 240 may comprise an optical detector 242,an adaptive amplitude controller (AAC) 244, a phase shifter 246, and avoltage-to-current (VI) converter 248.

The optical detector 242 may receive the second copy of the opticalsignal and convert the second copy into electrical voltage signals. Forexample, the optical detector 242 may be a positive intrinsic negative(PIN) diode, which may comprise an intrinsic semiconductor region inaddition to a plurality of other types of semiconductor regions. The PINdiode may be reverse biased using some external electrical bias signalto trap some of the optical signals' energies, or photons, passingthrough the intrinsic region. The trapped optical signals' energies maybe hence collected in the form of electrical voltage signals' energies.

The AAC 244 may be coupled to the optical detector 242 and may receivefrom the optical detector 242 a first copy of the collected voltagesignals. Specifically, the AAC may store the amplitude of eachconsecutive voltage signal and update an average amplitude for thecollected voltage signals. The AAC 244 may also compare the amplitude ofeach consecutive voltage signal with those of preceding voltage signalsand update a largest amplitude value and a smallest amplitude value forthe collected voltage signals. The AAC 244 may calculate a correctionvalue for each voltage signal, which may be equal to about the productof a constant and the difference between the stored amplitude of thevoltage signal and the updated average amplitude. The correction valuesmay be used, as described below, to adjust the amplitudes of the voltagesignals. The constant may be determined experimentally to allowequalizing of the input burst optical signals to the SOA with as muchamplitude difference as possible into optical signals output from theSOA with about equal optical amplitudes. For example, a plurality ofconstants may be used to calculate a plurality of correction values. Ofthose constants, the constant that results in substantial amplitudeequalization of optical signals with largest amplitude difference may beselected. The decision for selecting the experimental constant may bepartially influenced based on the updated maximum and minimum amplitudevalues. For example, the maximum amplitude value, minimum amplitudevalue, or both may be used to calculate a modified constant that may beabout equal or slightly different than the experimental constant.

The phase shifter 246 may be coupled to the optical detector 242 and theAAC 244. The phase shifter 246 may receive a second copy of thecollected voltage signals and the corresponding correction values fromthe optical detector 242 and the AAC 244, respectively. The phaseshifter 246 may invert the voltage signals by introducing a phase shiftin the voltage signals, for example at about 180°. The phase shiftedvoltage signal may have an opposite sign than that of the correspondingvoltage signal. In other words, when the voltage signal is positive, thephase shifted voltage signal may be negative, and vice-versa. The phaseshifted voltage may have an absolute amplitude about equal to that ofthe voltage signal. Additionally, the phase shifter 246 may adjust theabsolute amplitudes of the voltage signals by adding the correspondingcorrection values. For instance, the absolute voltage amplitude may bedecreased by an amount equal to the absolute correction value when theabsolute value of the voltage amplitude is smaller than the absolutevalue of the average voltage amplitude so that the corresponding inputoptical burst experiences more amplification in the OA. On the otherhand, the absolute amplitude may be increased by the amount equal to theabsolute correction value when the absolute voltage amplitude is largerthan the absolute average amplitude so that the corresponding inputoptical burst experiences less amplification in the OA. Consequently,the absolute voltage amplitudes may be about equal to the absoluteaverage amplitude and about equal to each other.

The VI converter 248 may be coupled to the phase shifter 246 and the OA230. The VI converter 248 may receive from the phase shifter 246 theinverted voltage signals. The VI converter 248 may convert the voltagesignals into current signals of proportional amplitudes. Subsequently,the current signals may have adaptive amplitude correction build in andmay be injected into the OA 240 to achieve maximum optical powerequalization. The injection current signals may arrive at the OA 230 atabout the same time as the first copy of optical signals, which may bedelayed by the ODL 220 for an amount of time. The amount of delay timemay be about equal to the amount of time required by the AIC controller240 to convert the second copy of the optical signals into the injectioncurrent signals. The VI converter 248 may also be a high speed VIconverter that converts voltage signals corresponding to optical burstsignals of relatively high frequencies into high frequency currentsignals.

In other embodiments, the AIC controlled OA 200 may additionally be usedto equalize or partially equalize the power of other optical signalsthat may not be optical burst signals including signals that may betransmitted upstream and downstream. In some embodiments, the OA 230 maybe substituted by another type of OA that may be controlled directly orindirectly using injection current signals. For instance, the currentsignals may be used to control a pump laser that may be coupled to anOA, such as an Erbium doped fiber amplifier (EDFA) or a Raman amplifier.The amplitudes of the pump laser output signals may be proportional tothe current signals amplitudes and may be used to control the OA opticalsignal amplification.

FIG. 3 illustrates an embodiment of an optical booster 300 that maycomprise an AIC controlled OA similar to the AIC controlled OA 200. Theoptical booster 300 may be coupled to the OLT 110 or the ODN 130 in thePON 100 and may be used to eliminate or reduce DC offset variations inthe optical receiver and thus improve optical signals' reception in thePON 100. The optical booster 300 may also be used to compensate forsignal losses in long-reach PON systems with relatively long distancesalong the ODN and in wide-reach PON systems comprising relatively largenumbers of ONUs. The optical booster 300 may comprise a first wavelengthdivision multiplexer (WDM) 310, an OA 320, a second WDM 330, and an AICcontrolled OA 340.

The first WDM 310 may be coupled to the OA 320 and the AIC controlled OA340. The first WDM 310 may route the optical signals downstream from theOLT 110 to the OA 320 at a first wavelength or wavelength channel. Thefirst WDM 310 may also forward upstream the optical signals at a secondwavelength or wavelength channel from the AIC controlled OA 340. Forinstance, the first WDM 310 may be an optical filter that may separatethe optical signals transmitted downstream at a first wavelength equalto about 1490 nanometers (nm) from the optical signals transmittedupstream at a second wavelength equal to about 1310 nm.

The OA 320 may receive the optical signals transmitted downstream at thefirst wavelength or wavelength channel, amplify each optical signalpower proportionally with or without power equalization, and forward theoptical signals downstream. As such, the OA 320 may be any of the OAsdescribed herein. In addition, the OA 320 may be configured to amplifyoptical signals transmitted over the C-band channel comprisingwavelengths between about 1530 nm to about 1565 nm or the S-band channelcomprising wavelengths between about 1460 nm to about 1530 nm.

The second WDM 330 may be coupled to the OA 320 and may be configured toforward the optical signals transmitted downstream at the firstwavelength or wavelength channel from the OA 320. The second WDM 330 mayalso be coupled to the AIC controlled OA 340 and may be configured toforward the optical signals transmitted upstream at the secondwavelength or wavelength channel to the AIC controlled OA 340. Thesecond WDM 330 may be an optical filter configured similar to the secondWDM 310 and may separate the optical signals transmitted at about 1490nm from the optical signals transmitted at about 1310 nm.

The AIC controlled OA 340 may receive the optical signals transmittedupstream at the second wavelength or wavelength channel, which mayinclude optical burst signals. The AIC controlled OA 340 may be similarto the AIC controlled OA described above, and thus may adaptivelyamplify the optical signals at about equal power and forward theamplified optical signals upstream. The OA 340 may be configured toamplify optical signals transmitted over the O-band comprisingwavelengths between about 1260 nm to about 1360 nm.

FIG. 4 illustrates an embodiment of an integrated optical receiver andtransmitter system 400 in OLT 110 that may comprise an AIC controlled OAsimilar to the AIC controlled OA 200 as a pre-amplifier. The integratedsystem 400 may be coupled to the OLT 110 to improve upstream opticalsignals reception in the PON 100. By improving reception for upstreamsignals, the integrated system 400 may facilitate symmetricbidirectional communications at high data rate such as 10 Gbps, wherethe transmission bandwidth for upstream signals may match or approachthe bandwidth for downstream signals. The integrated system 400 maycomprise a WDM 410, an AIC controlled OA 420, an optical receiver 430,and an optical transmitter 440.

The WDM 410 may be coupled to the AIC controlled OA 420 and the opticaltransmitter 440. The WDM 410 may route downstream the optical signalstransmitted downstream from the optical transmitter 440 at a firstwavelength (1490 nm) or wavelength channel, and route the opticalsignals transmitted upstream from the ONUs 120 to the AIC controlled OA420 at a second wavelength (1310 nm) or wavelength channel. For example,the WDM 410 may be an optical filter that may separate the opticalsignals transmitted upstream at about 1310 nm from the optical signalstransmitted downstream at about 1490 nm. The AIC controlled OA 420 mayreceive the optical signals transmitted upstream at the secondwavelength or wavelength channel, which may include optical burstsignals. The AIC controlled OA 340 or 420 may adaptively amplify theoptical signals at about equal power and send the amplified opticalsignals to the optical receiver 430.

In one embodiment, the optical receiver 430 and the optical transmitter440 may receive and transmit, respectively, the optical signals atdifferent bandwidths and different wavelengths or wavelength channels.In another embodiment, the optical receiver 430 and the opticaltransmitter 440 may receive and transmit, respectively, the opticalsignals at about equal bandwidths. For instance, the optical receiver430 may receive the amplified optical burst signals from the AICcontrolled OA 420 at about 10 Gbps and a wavelength of about 1310 nm.Similarly, the optical transmitter 440 may transmit optical signalsdownstream at about 10 Gbps but at a wavelength of about 1490 nm. In anembodiment, the optical transmitter 440 may transmit optical signals atabout 5 decibels per milliwatt (dBm), such as a distributed feedback(DFB) laser.

FIG. 5 illustrates an embodiment of an OLT 500 that may be used inwide-reach PON systems comprising up to about 256 ONUs. The OLT 500 maycommunicate with the ONUs by transmitting and receiving optical signalsusing two different downstream and upstream channels, respectively. TheOLT 500 may comprise an optical transmitter 510, an optical attenuator520, an OA 530, a WDM 540, an AIC controlled OA 550, and an opticalreceiver 560. In an embodiment, the optical transmitter 510, which maybe like any of the optical transmitters described herein, may transmitthe optical signals downstream at about 10 Gbps and over the C-bandchannel. The optical attenuator 520 may be coupled to the opticaltransmitter 510 and may be an absorptive, reflective, or another type ofattenuator. The optical attenuator 520 may reduce the optical signals'power prior to sending the optical signals to the OA 530, which may benecessary to prevent saturation at the OA 530. Otherwise, excessivepower levels in the optical signals may saturate the OA 530 and preventproper signal amplification. The OA 530, which may be like any of theOAs described herein, may receive the attenuated optical signals fromthe optical attenuator 520, amplify the attenuated optical signals andforward the optical signals to the WDM 540. The WDM 540 may receive theamplified optical signals and route the signals downstream to the ONUs.Amplifying the optical signals using the OA 530 may compensate forreduced powers in the signals received at the ONUs due to signalsplitting along the branches of the ODN.

The WDM 540 may also receive optical signals, including optical burstsignals, from the ONUs at a wavelength of about 1310 nm and forward thesignals to the AIC controlled OA 550. The AIC controlled OA 550 mayadaptively amplify the optical signals and forward the signals to theoptical receiver 560 over the O-band channel. The optical receiver 560may hence receive the optical signals with about equal amplitude, whichmay reduce the DC offset in the optical receiver and enable upstreamsignal detection at similar rates as in downstream signals and up toabout 10 Gbps.

FIG. 6 illustrates an embodiment of a wide-reach PON 600. The PON 600may comprise an OLT 610, a splitter 620, and up to about 64 ONUs 630.The OLT 610 may comprise an integrated optical receiver and transmittersystem, similar to the integrated system 400. Hence, the OLT 610 maytransmit and receive downstream and upstream signals, respectively, atabout equal bandwidths, for example at 10 Gbps. The OLT 610 may alsocomprise an optical transmitter 612 that may be like any of the opticaltransmitters described herein. The optical transmitter 612 may transmitthe optical signals downstream with sufficient power and without furthersignal amplification to compensate for power losses due to splitting atthe splitter 620. The splitter 620 may receive the optical signals fromthe OLT 610, split the signals into a plurality of copies, and forwardeach copy downstream to one of the ONUs 630. Each ONU 630 may receive acopy of the optical signals comprising a portion of the power of theoriginal optical signals. The splitter 620 may also forward upstreamsignals, including optical burst signals, from each of the ONUs 630 tothe OLT 610.

In some embodiments, the PON 600 may be a long and wide-reach PON withover about 60 km of fibers along the ODN. The PON 600 may comprise anoptical booster 640, similar to the optical booster 300, which may belocated between the OLT 610 and the splitter 620 or at any otherlocation in the ODN. The optical booster 640 may further amplify thesignals transmitted downstream prior to splitting the signals into aplurality of copies and forwarding the signals to the ONUs 630. Furtheramplifying the signals may compensate for additional power losses due tosignal attenuations over long travel distances in the fibers. Theoptical booster may also adaptively amplify the optical burst signalstransmitted upstream from the ONUs 630 before forwarding the signals tothe OLT 610. The PON 600 may comprise additional optical boosters tocompensate for additional losses introduced by longer length of fibers.

FIG. 7 illustrates another embodiment of a long & wide-reach PON 700.The PON 700 may comprise an OLT 710, a splitter 720, up to about 256ONUs 730, and at least one optical booster 740 to extend the reach toabout 60 km of fiber. The OLT 710 may be a wide-reach OLT similar to theOLT 500 and capable of transmitting and receiving downstream andupstream signals, respectively, at about equal bandwidths, such as at 10Gbps. The OLT 710 may transmit the downstream signals with sufficientpower to compensate for power reductions in the copies forwarded to eachof the 256 ONUs 730. The PON 700 may also comprise additional opticalboosters 740 for longer length of fibers.

FIG. 8 illustrates one embodiment of an AIC controlled optical burstmode method 800. The method 800 may be implemented at the AIC controlledOA 200 to obtain the injection currents based on the power of opticalburst signals and use the injection currents to amplify the opticalsignals. FIG. 9 illustrates a schematic diagram of converted andamplified signals 900 using the method 800. The signals 900 may compriseoptical burst signals 910, voltage signals 920, inverted voltage signals930, and adjusted voltage signals 940.

Returning to FIG. 8, at block 810 the method 800 may split the opticalburst signals into two copies comprising optical burst signals similarto the original signals. The first copy may have a larger power levelthan the second copy. At block 820, the method 800 may delay thetransmission of the first copy of optical burst signals. At block 830,the method 800 may convert the optical burst signals in the second copyto electrical voltage signals. In FIG. 9, the optical burst signals 910may represent the second copy of optical burst signals, while thevoltage signals 920 may represent the converted electrical voltagesignals.

At block 840 of FIG. 8, the method 800 may further split the electricalvoltage signals into two copies that may be similar. At block 850, themethod 800 may calculate an amplitude correction value for each voltagesignal in the first copy, which may be about equal to the differencebetween the amplitude of each voltage signal and the average amplitudein all voltage signals times a constant which is determined byexperiment. At block 860, the method may invert the amplitudes of thevoltage signals in the second copy by introducing a phase shift angle,which may be equal to 180°, to each signal. At block 870, the method 800may adjust the voltage signals' amplitudes by adding the amplitudecorrection values (may be positive or negative) to the absoluteamplitudes of the corresponding inverted voltage signals. In FIG. 9, theinverted voltage signals 930 and the adjusted voltage signals 940 mayrepresent the inverted signals and the adjusted signals, respectively,in the second copy.

At block 880 of FIG. 8, the method 800 may convert the adjusted voltagesignals into injection current signals that may have proportionalamplitudes to those in the adjusted voltage signals. At block 890, themethod 800 may amplify the delayed optical burst signals in the firstcopy proportionally to the amplitudes of the corresponding injectioncurrents signals. Thus, each optical burst signal may be amplifiedproportionally to a different current signal amplitude, such that theoptical burst signals with higher power levels may be amplified bysmaller amounts than those with lower power levels. Furthermore, theamount of amplification determined by the correction value may result inamplifying each optical burst signal to about the average power in allthe optical burst signals. Consequently, the power levels in theamplified optical burst signals may be about equal and the DC offsetvariations may be reduced in the optical receiver.

In another embodiment, the method 800 may adjust the amplitudes of thevoltage signals at block 870 before inverting the voltage amplitudes atblock 860. The method 800 may also implement blocks 860 and 870simultaneously by introducing an appropriate phase shift angle to eachvoltage signal. The method 800 may amplify optical signals that may notbe transmitted continuously without interruptions or pauses and may notcomprise optical burst signals.

The network components described above may be implemented on anygeneral-purpose network component, such as a computer or networkcomponent with sufficient processing power, memory resources, andnetwork throughput capability to handle the necessary workload placedupon it. FIG. 10 illustrates a typical, general-purpose networkcomponent suitable for implementing one or more embodiments of a nodedisclosed herein. The network component 1000 includes a processor 1002(which may be referred to as a central processor unit or CPU) that is incommunication with memory devices including secondary storage 1004, readonly memory (ROM) 1006, random access memory (RAM) 1008, input/output(I/O) devices 1010, and network connectivity devices 1012. The processormay be implemented as one or more CPU chips, or may be part of one ormore application specific integrated circuits (ASICs).

The secondary storage 1004 is typically comprised of one or more diskdrives or tape drives and is used for non-volatile storage of data andas an over-flow data storage device if RAM 408 is not large enough tohold all working data. Secondary storage 1004 may be used to storeprograms that are loaded into RAM 1008 when such programs are selectedfor execution. The ROM 1006 is used to store instructions and perhapsdata that are read during program execution. ROM 1006 is a non-volatilememory device that typically has a small memory capacity relative to thelarger memory capacity of secondary storage 1004. The RAM 1008 is usedto store volatile data and perhaps to store instructions. Access to bothROM 1006 and RAM 1008 is typically faster than to secondary storage1004.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. An apparatus comprising: at least one componentconfigured to: convert an optical signal into a voltage signal;calculate an amplitude correction value for the voltage signal; invertan amplitude of the voltage signal; adjust the amplitude of the invertedvoltage signal according to the amplitude correction value; convert theadjusted voltage signal into a current signal; and use the currentsignal to control at least one semiconductor optical amplifier (SOA). 2.The apparatus of claim 1, wherein the at least one component is furtherconfigured to: split the optical signal into a first portion and asecond portion, wherein the second portion is converted into a voltagesignal; and amplify the first portion proportionally to the amplitude ofthe current signal.
 3. The apparatus of claim 2, wherein the at leastone component is further configured to delay the first portion by a timeabout equal to the time required to convert the optical signal into avoltage signal, calculate the amplitude correction value, invert theamplitude of the voltage signal, and adjust the amplitude of theinverted voltage signal.
 4. The apparatus of claim 3, wherein the atleast one component is further configured to split the voltage signalinto a first copy and a second copy, wherein the first copy is used tocalculate the amplitude correction value, and wherein the second copy isinverted, adjusted and converted into the current signal.
 5. Theapparatus of claim 1, wherein the amplitude correction value is aboutequal to a product of an experimental constant and a difference betweenthe amplitude of the voltage signal and an average amplitude of aplurality of previous voltage signals corresponding to a plurality ofprevious optical signals.
 6. The apparatus of claim 5, wherein theexperimental constant results in about equal power amplification foroptical signals with increased amplitude variations.
 7. The apparatus ofclaim 6, wherein the experimental constant is at least partiallydetermined based on the lowest amplitude and the highest amplitude ofthe previous voltage signals.
 8. The apparatus of claim 1, wherein theapparatus is part of a passive optical network (PON) opticaldistribution network (ODN).
 9. The apparatus of claim 1, wherein theapparatus is part of a passive optical network (PON) optical lineterminal (OLT).
 10. A method comprising: converting an optical signalinto a voltage signal; calculating an amplitude correction value for thevoltage signal; inverting an amplitude of the voltage signal; adjustingthe amplitude of the inverted voltage signal according to the amplitudecorrection value; converting the adjusted voltage signal into a currentsignal; and using the current signal to control at least onesemiconductor optical amplifier (SOA).
 11. The method of claim 10,further comprising: splitting the optical signal into a first portionand a second portion, wherein the second portion is converted into avoltage signal; and amplifying the first portion proportionally to theamplitude of the current signal.
 12. The method of claim 11, furthercomprising splitting the voltage signal into a first copy and a secondcopy, wherein the first copy is used to calculate the amplitudecorrection value, and wherein the second copy is inverted, adjusted andconverted into the current signal.
 13. The method of claim 12, furthercomprising delaying the second portion by a time about equal to the timerequired to calculate the amplitude correction value of the firstvoltage signal.
 14. The method of claim 13, wherein the amplitudecorrection value is about equal to a product of an experimental constantand a difference between the amplitude of the voltage signal and anaverage amplitude of a plurality of previous voltage signalscorresponding to a plurality of previous optical signals.
 15. The methodof claim 14, wherein the experimental constant results in about equalpower amplification for optical signals with increased amplitudevariations.
 16. The method of claim 15, wherein the experimentalconstant is at least partially determined based on the lowest amplitudeand the highest amplitude of the previous voltage signals.
 17. A methodimplemented at an adaptive injection current (AIC) controller in apassive optical network (PON), the method comprising: splitting aplurality of PON optical burst signals into a first and second copy ofoptical burst signals; converting the second copy of the PON opticalburst signals into electrical voltage signals; splitting the electricalvoltage signals into a first and second copy of electrical voltagesignals; calculating an amplitude correction value for each electricalvoltage signal in at least one of the first and second copies ofelectrical voltage signals; inverting an amplitude of each electricalvoltage signal in the at least one copy of electrical voltage signals;adjusting the amplitude of each electrical voltage signals according tothe amplitude correction value; and converting the adjusted electricalvoltage signals into injection current signals.
 18. The method of claimof claim 17, further comprising: delaying transmission of the first copyof the PON optical burst signals; and amplifying the delayed opticalburst signals.
 19. The method of claim 18, wherein the delayed opticalburst signals are amplified proportionally to the amplitudes ofcorresponding injection current signals.
 20. The method of claim 17,wherein the amplitudes of the electrical voltage signals are inverted byintroducing a phase shift angle.
 21. The method of claim 17, wherein theinjection current signals have amplitudes proportional to the amplitudesof the adjusted electrical voltage signals.
 22. The method of claim 17,further comprising amplifying each optical burst signal proportionallyto a different current signal amplitude such that the PON optical burstsignals with higher power levels are amplified by smaller amounts thanthe PON optical burst signals with lower power levels.